For the diagnosis of circulation diseases it is effective to measure the blood flow velocity of an aorta and the blood flow volume thereof in addition to electrocardiogram measurement, blood flow measurement, pulse wave analyses, so on. A method which has been conventionally used for measuring blood flow velocity and blood flow volume of aortas is blood vessel catheter measuring method in which a catheter is inserted into an aorta. In this method, a pair of pressure sensors are attached at a set interval to the leading end of the catheter. The catheter is inserted until its leading end reaches an aorta under X-ray inspection to detect pulse waves as a pressure change by both pressure sensors, whereby a blood flow velocity of the aorta is obtained based on a phase difference of the detected pulse waves. A blood flow volume is given by multiplying a blood flow effective sectional area of the aorta by the blood flow velocity. In a different practiced method, a reagent is poured from the leading end of the catheter to measure a lung circulation time of the reagent, whereby an averaged stroke volume per minute is given.
But these invasive blood vessel catheter measuring methods are large scaled by inserting a catheter into an aorta, which unpreferably much burdens patients physically and mentally. An additional problem is that the measuring apparatus is accordingly expensive and is not easily operable for the measurement and requires special skill. Further another problem of the method in which a reagent is poured is that the poured reagent burdens patients.